Walter



W. 0. LUM.

MOTOR CONTROL SYSTEM.

APPLICATION FILED 00123. 1913.

1 1 96, 1 24:. Patented Aug. 29, 1916.

INV NTOR m @vm ATTORNEY UNITED STATES PATENT OFFICE.

WALTER 0. LUM, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Patented A11 29, 1916.

Application filed October 3,1913. Serial No. 793,260.

To all whom it may concern:

Be it known that I, HLTER O. LUM,

a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a specification.

My invention relates to motor-control systems, and it has special reference to systoms of control in which staiting resistors are controlled by sets of automatically. operated switches.

My invention has for one of its objects to provide a system of control which will. be entirely automatic in its action and which will operate to cut out'steps of the starting resistor in a predeterminedorder.

A further object of my invention is to provide a system of field control in which a single current-limit device may be employed both fol-retarding and for accelerating a motor.

In the operation of motors for driving plane-rs, elevators and similar machinery requiring frequent stops and reversals, it is desirable that a system of control be employed that permits of rapid acceleration instarting and provides means for bringing the motor to-a stop quickly and safely. 1t is essential to provide a system .which is entirely autoinatic'in its operation in order that the loss of time and the attention required in manually operated systems may be avoided.

My invention consists of a plurality of successively actuated f switches which controllthe sections of the starting-resistor ofa motor circuitf Each-of the actuatingcoils of the several switches is connected in the controlled circuit by the operation of. the.

'ing 5 and the resistor 6' to the conductor by a. resistor 6. A sectional resistor 7, which is adapted to be connected in series witl. the armature 4r, is controlled by a series of successively actuated electromagnetic switches S, 9, l0 and 11 which comprise actuatmg coils 12, 13, ll, 15, respectively. The coil 1? acts also as a holding coil for the switch 8, while switches 9, 1U, 11 are provided with holding coils 1G, 17, 1S.

Ashort circuit for the resistor is con: trolled: by a current-limit switch 'land a reverse-current relay switch :20 which. are connected in'parallel circuits. The switch 19 is controlled by a. coil 21 that is in series 'withthe armature l. The switch 20 is con trolled by'a coil 22, also in. series with the armature l, and .by a shunt coil which is wound to oppose the. series coil 22. The parallel circuits of the switches 19 and 20 are controlled by 'a manually operated switch 24'.

To start the motor, the switch 2i is moved to its upper position and a main switch is closed. Current flows through a circuit which: extends from the line conductor 2 through the SWli'Cll'QQ COil 12, resistor T. armature l, coils 21 and 22 conductor 2% and switch to theline-conductor 1;. Current also flows through the shunt field wii The-coil 12 will-be energized to close illw switch '8 and thereby complete a short circuit throughthe coil '13 fo -one section oi. the resistor .7. The coil .12 acts as a holding coilfor.t'he'switchS until the coil 13 has closed the switch 9 and thereby short circuited the will? and the switch 8, allow-1 mg the latter to open. The closing of the switch 9 establishes a short circuit for a end section of the resistor 7 through the holding coil 16 and the actuating coil 14. The switches 10 and 1.1 are then closed in order and a'short circuit for thelen'ti -e resister 7 is established. through the holding coil 18, thus insuring that the switch 11 will remain closed until the motor circuit is broken.

. increase value, the switch is thrown to its lower position. braking circuit will then be established When themotor is being accelerated, the switch 20 is in its closed position, because current flows through. the oppositely wound coils and in the same direction. In this position of. the switch 20, a short circuit ,is established for a pair of contacts 2? controlled by the switch 19.. As long as the armature current does not rise above a predetermined value, the, switch 19 remainsin its lower position and the resistor 6 is in series with the shunt field winding 5. \Vhen th armature current exceeds the value for which the switch 19 is adjusted, the coil21 drawsthe switch upwardly to bridge a pair of contact members 28 and. thereby short circuit the resistor 6 through the contact memhers 29 of the switch 24. The result is to strengthen the field of the motor and thus the counter 'electromotive of the hen the current falls to a normal 19 again opens the short circuit to weaken the field of the motor and thus further accelerate the motor. The oscillations of the switch 19 will continue as long as the armature current fluctuates above the predetermined value.

\Vhen it is desired to main switch 25 is opened and the switch 21' A dynamic motor.

from the motor armature & through the coils 21., 22 and back to the armature. Current' generated by the motor armature now flows in reverse directions through the coils 22 and 23, and the switch 20 is opened to break the short circuit for contact members 27 of the switch 19. Current also flows through a shunt circuit comprising the shunt field winding 5, contact members 30 of the switch 2%, contact members 27 of the switch 19 and conductors 31 and32. When the switch 2% is thrown to its lower position, "the circuit comprising the contact members 28 of the switch 19 is broken, and a short circuit for the resistor 6 is controlled by the switch 19 and the contact members 27,

When the current in the dynamic braking circuitexceeds the predetermined value at which the switch 19 operates, the latter breaks the short circuit for the resistor 6 which includes the contact members 27 The resistor 6 is inserted in series with the field Winding 5 to weaken the motor field and thereby decrease the armature current. When the current falls below the predetermined value, the switch 19 falls to, clos the short circuit again and thereby strengthen the field of the motor to produce the maximum braking current. This operation, of the switch continues until the current has fallen permanently below the predetermined value or until th motor has been brought to a stop.

By means of this arrangement, I and en parts.

stop the motor, the.

abled to accelerate and retard motors within the shortest time possible consistent with safety. The currentlimit switch insures that the current values will never become excessive but that, on the other hand, a maximum safe current will be employed both for acceleration and retardation of the motor armature.

A modificationis shown in Fig. like numerals designate corresponding The switch 2i is so arranged as to be operated automatically instead of manually as in the system of Fig. 1. 2% is provided with a coil 33 which is connected across the motor terminals. The switch "20 is provided with a pair of contact members 31 which are connected to the re spective terminals of the coil IVhen the main switch 25 is closed and the switch 19 is in its lower position, the shunt coil 33 is energized to hold the switch 24: in its'upper position. The several switches are then in their proper respective positions for accelerating the motor. The operation of the system differs in no other material respect from that of the system shown in Fig. 1.

\Vhen the dynamic braking circuit is established, the reverse-current relay switch 20 is moved to its upper position, as above explained in connection with Fig. 1, and the coil 33 is shor't-circuited, allowing the switch 2% to drop into its lower position. The

switches 20 and 24 then occupy their proper respective positions for dynamic braking which is accomplished in the same manner as above described. 7

I claim as my invention:

1. In a control system, the combination with a motor, and a. field resistor therefor,

of a current-limit device for controlling said resistor and means for reversing the efl'ects, produced by the operation of said current-limit device.

2. In a. control system, the combination with a motor, and a field resistor therefor, of a current-limit switch for controlling said resistor, and means comprising a reverse-current relay switch for controlling.

duced by the operation of one of said switches. I

5. In a control system, the combination The switch with a dynamo-electric machine and a field resistor theretor, of a current-l1mit switch for automatically short circuiting said resistor when said dynamo-electric machine opcrates as amotor and for automaticaily brealv iir the short circuit when said dynamoelectric :rmzchine operates as a generator.

6. In a control system, the combination with a. motor, of a switch for controlling the field strength oi said motor and means controlled by the direction of current through the armature of said motor for corn trolling the effects produced by the operation of said switch. 7

7. In a control. system, the combination with a motor and a field resistor therefor, of a current-limit switch for controlling said resistor, and means for reversing the effect of said current-limit switch comprising a plurality of switches, one of which comprises a plurality of coils wound to assist each other when connected in series.

8. In a control syst n, the combination with a motor and a iii-id resistor therefor, of a current-limit sw shunt circuit for said r braking circuit for said motor, and means for reversing the effect of said switch when said braking circuit is established.

9. In a control system, the combination with a motor and a field resistor therefor, of a double-throw switch for controlling said resistor, means for rendering the switch inoperative in one of its positions when the motor is being accelerated and inesistor, a dynamicoperative in its other position when the motor is being retarded.

10. In a motor-control system, the combination with an electric motor having a shunt field magnet winding, and a resistor in circuit therewith, of a. switch for controlling a shunt circuit for said resistor, and means comprisinga double-throw relay, switch for reversing the efi'ects produced by the operation of said controlling switch.

11.- In a motor-control system, the combilimit switch for 1 for controlling a nation with an electric motor having a shunt field magnet winding and a resi tor in cir cuit therewith, of a pair of circuits shunt relation with said resistor, and a pair of doublethrow switches for controlling said circuits, one of said switches determining, by its position, the function of the other switch.

1:2. In a motor-control i, bination with an electric 1.1 tor shunt field magnet winding and in circuit with said windir harm a resistor I of a current-- controllin a shunt circuit for said resistor, and means doub1e-throw reverse-current re for controlling the functions of rent-limit switch. I

13. In a motor-control system, the combi nation with an electric motor having a field magnet winding, and a resistor in circuit with said winding, of a current-limit switch for controlling a shunt circuit for said resistor, and a double-throw relay switch which operates, according to its position, to cause the currcntlimit switch to respectively close and open said shunt ciriy switch said curcomprising a cuit when said currentlimit switch is in its normal position.

l i. In a motor-control system, the combination with an electric motor having a field magnet winding, and a resistor in circuit with said winding, of a current-limit switch for controlling a shunt circuit for said resistor, and a double-throw relay switch which operates, according to its position, to cause the current-limit switch to respectively open or close the shunt circuit when said current-limit switch is in tion. I

In testimony whereof, I have hereunto subscribed my name this 26th day of Sept,

WALTER o. LUM;

its open posi- IVitnesses i C. E. .STEPHENS, B. B, 

